The present invention relates to a preheat indicator for use with ceramic foam filters and a method for forming the indicator. The indicator is primarily used in molten metal filter applications to show that the filter has been preheated to a desired temperature so that filtration of molten metal can commence.
Ceramic filter bodies have been used commercially in the filtration of molten metals such as molten iron and molten aluminum for quite some time. U.S. Pat. Nos. 3,893,917 and 3,947,363, both to Pryor et al., 4,081,371 to Yarwood et al. and 4,331,621 to Brockmeyer illustrate some of the ceramic bodies used to filter molten metals.
Such ceramic filter bodies are normally preheated prior to commencement of molten metal filtration to protect the filter body from a thermal shock point of view and to expand gasket materials surrounding the filter. Improperly heated filters can result in the following problems:
1. metal bypass due to incomplete expansion of the expandable gasket;
2. filter breakage due to thermal shock;
3. metal freezing due to a cold filter body receiving near solidification point melt;
4. filter breakage in cases of uneven filter support due to uneven pressure exerted on the filter body by higher than usual priming head caused by filtration attempt through a cold filter; and
5. introduction of hydrogen ions into the melt through gasket gas byproducts.
Preheating, if done correctly can minimize these problems and clear the way for a clean, safe, efficient filtration. However, this simple task may not always be done properly. For example, the burners may not heat the filter to the desired temperature due to burner inefficiency or they may not heat the filter uniformly across its width.
As yet, there is no commercially available filter body having a mechanism for providing a signal of any type which shows that the filter body has been adequately preheated and filtration can now be commenced. The present invention overcomes this shortcoming through the provision of a preheat indicator for molten metal filter bodies.
Accordingly, it is an object of the present invention to provide a preheat indicator for ceramic body molten metal filters which signals that the ceramic body has been preheated to a desired temperature.
It is a further object of the present invention to provide a preheat indicator as above which signals that the body has been substantially uniformly heated across its width.
It is yet a further object of the present invention to provide a preheat indicator as above which is relatively simple to apply to a ceramic filter body and to use.
These and further objects and advantages will become more apparent from the following description and drawings in which like reference numerals depict like elements.